1. Field of the Invention
The present invention relates in general to an image forming such as a color laser printer.
2. Discussion of Related Art
A conventional image forming apparatus such as a color laser printer is arranged to form a static latent image on a surface of an image carrier such as a photosensitive or photoconductive drum, and apply a toner to the surface of the image carrier, for thereby forming a toner image on the image carrier. This process is repeated for each of four toner images of different colors, which are formed on the respective image carriers, using respective yellow (Y), magenta (M), cyan (C) and black (K) toners, so that a color image is formed on a recording medium such as a sheet of paper, with the toner images of different colors being sequentially transferred from the respective image carriers to the recording medium.
The toner image of each color is transmitted from the corresponding image carrier directly to the recording medium while the recording medium is fed by a conveyor belt, or indirectly to the recording medium via an intermediate image transfer belt. In the latter method, the toner images of different colors are first transferred from the image carriers to the intermediate image transfer belt, to form the color image on the transfer belt, and the thus formed color image is transferred from the transfer belt to the recording medium. In either of these two methods, the toners inevitably remain on the surfaces of the image carriers after the toner images are transferred the surfaces.
To remove the remaining toner from each image carrier, the conventional image forming apparatus is provided with a cleaner mechanism such as a blade device, which is arranged to remove the toner by scraping the surface of the image carrier. Alternatively, a developing device of the image forming apparatus which includes a developing roller operable to apply the toner to the surface of the image carrier is electrically controlled such that a portion of the toner which remains on the image carrier and which does not form the toner image is adsorbed onto the surface of the developing roller. In the latter case, the image forming apparatus which is not provided with a cleaner mechanism may be referred to as a “cleanerless type” image forming apparatus”. An example of this cleanerless type is disclosed in JP-3154757B2 (JP-5053482A).
The image forming apparatus of the cleanerless type is advantageous in that the size of the apparatus can be reduced in the absence of a cleaner mechanism for removing the remaining toner from the surface of the image carrier. However, the apparatus still suffers from difficulty to remove paper dust which tends to adhere to the surface of the image carrier during a transfer of the toner image from the image carrier to the recording medium. In the presence of the paper dust on the image carrier, the toner may adhere to the paper dust and may be transferred together with the paper dust to the recording medium, giving rise to a risk of undesirable formation of unintended colored spots (generally called “paper dust spots”) on the recording medium.
That is, the paper dust produced by the recording medium in the form of paper sheets tends to adhere directly to the image carrier, or indirectly to the image carrier via the intermediate image transfer belt. In the image forming apparatus of the cleanerless type, the paper dust cannot be removed from the image carrier, leading to the risk of formation of the paper dust spots on the recording medium.